Optical properties of quasi-tetragonal BiFeO3 thin films

Abstract

Optical transmission spectroscopy and spectroscopic ellipsometry were used to extract the optical properties of an epitaxially grown quasi-tetragonal BiFeO 3 thin film in the near infrared to near ultraviolet range. The absorption spectrum is overall blue shifted compared with that of rhombohedral BiFeO 3 , with an absorption onset near 2.25 eV, a direct 3.1 eV band gap, and charge transfer excitations that are ϳ0.4 eV higher than those of the rhombohedral counterpart. We interpret these results in terms of structural strain and local symmetry breaking.

Structural dependent ultrafast electron-phonon coupling in multiferroic BiFeO3 films

“…A slight tetragonal distortion reduces the space group to P4mm and modifies the overall perovskite structure, therefore the local Fe 3þ environment is quasi-square pyramidal. 7,25 One of the Fe-O axial distances increases to $2.80 Å , and the Fe-O equatorial bond lengths are reduced to $1.93 Å owing to the structure strain and symmetry breaking. 25 The pure tetragonal phase with small monoclinic distortion can be stabilized by the large epitaxial stain.…”

“…[1][2][3] Due to large ferroelectric polarization of $100 lC/cm 2 , magneto-electric coupling, and the possibility of epitaxial strain engineering of magneto-electric properties, BFO has attracted enormous attention. [4][5][6][7] Recently, a tetragonal BFO has been of great interest, not only as it potentially possesses a giant polarization and enhanced electromechanical response, 8 but also it provides a unique example of a concurrent magnetic and ferroelectric transition at near room temperature. 9 From the applied point of view in photonics, it has been proposed that terahertz radiation from BFO films can be used in ferroelectric domain imaging and optical readout of the state of ferroelectric memories.…”

Electronic Band Structures and Phase Transitions of Ferroelectric and Multiferroic Oxides

“…Based on the theoretical calculations and experimental observations, the four energy bands can be uniquely assigned to the following electronic transitions: (1) [51][52][53][54][55] Within the experimental error bars, the energy positions shift toward the higher energy at the temperature of 5.3 K except for the second excitation, which can be attributed to the energy band variations. Nevertheless, the origin of the abnormal shift for the second excitation is unclear in the present work.…”

“…Under the influence of the tetrahedral crystal field, the Fe 3d orbital states split into t 2g and e g state and the t 2g state strongly hybrided with the O p orbital. [52] With decreasing the temperature, the t 2g and e g states can be located at different level in the energy space, which can affect the electronic excited ability of the Bi, Fe, and O states. On the other hand, the evaluated optical constants of the BFO film is presented in Fig.…”

Low-dimensional nanostructured photocatalysts

“…Moreover, abnormal properties can be induced by the heterointerface in thin film. Previous studies have shown that the nature of the substrate can influence on crystal phase and optical or PC properties of thin film, like the band gap shift or phase change, which could be used to modify the PC properties of the films [6,[68][69][70][71].…”